A typical digital video surveillance system comprises at least two types of wire networks, a first type of wire network for data transport, and a second type of wire network for power distribution to digital cameras in the system.
It may be useful, for example for saving costs, to use a same wire infrastructure able to distribute both data and power.
Technologies which allow both data and power to be carried over a same wire are known as “Power over Ethernet” (PoE) technologies. These technologies allow power distribution and Ethernet data to be mixed on one cable.
It is advantageous, in terms of cost among others, to build a new digital camera surveillance infrastructure by using LAN wires which are able to support power distribution.
Moreover, an analogue camera surveillance system may be upgraded in order to build a digital video surveillance system. Some analogue camera surveillance systems use for example coaxial cables to transport data from the analogue cameras to a central point. Some technologies, such as IP over Coax technologies, allow transport of both data and power over existing analogue video distribution cable networks, such as Coaxial or copper pair wire networks.
An analogue camera surveillance system is upgraded or retrofitted in order to build a digital camera surveillance system by replacing analogue cameras by digital network cameras, for example IP cameras, and by inserting an adapter, both at the central point and at each digital camera, the analogue cable infrastructure being reused.
In a retrofit digital video surveillance system, the central point is connected to an Ethernet infrastructure (for example a LAN) and to a plurality of digital cameras through coaxial cables.
The adapter in the central point converts data originating from the Ethernet infrastructure to data adapted to be transported by the coaxial cables (“IP Coax Traffic”) and sends it to the digital cameras (such as “IP Coax cameras”), converts data originating from digital cameras to data adapted to be transported by the Ethernet infrastructure (“Ethernet Traffic”) and sends it to the LAN, and provides power to the IP cameras over the coaxial cables.
The adapter in the camera (“Coax terminal adapter”) is connected to an Ethernet port of the camera. The “Coax terminal adapter” converts IP Coax traffic originating from the Coaxial cable to Ethernet traffic and sends it to the camera, converts Ethernet traffic originating from the camera to IP Coax Traffic and sends it to the Coaxial cable, and receives power from the Coaxial cable and delivers it to the camera through the Ethernet port.
In these technologies, the Coax terminal adapter comprises a power management module configured for managing the power distribution to the camera. In particular, the power management module is configured for delivering power to the camera following standards for power transport over Ethernet known as PoE (IEEE802.3af) or PoE+ (IEEE802.3at).
By implementing these standards a power source device or item of power sourcing equipment (PSE), does not deliver power to a non-compatible power sink device (PD). Furthermore, a power source device only delivers power to a compatible power sink device, if it is able to provide the amount of power needed by the power sink device.
Thus, a Coax terminal adapter (in particular the power management module) determines whether the camera is compatible with PoE standards, and if the response is positive, it determines the maximum power consumption of the camera or camera power class. According to PoE standards, the power management module only delivers power to the camera if the camera is compatible with PoE standards and if the power management module is able to deliver the maximum power consumed by the camera, i.e. that the camera may be started-up in its power class.
For example, document US2010/0031066 describes a system for determining a class of power delivered by an item of power sourcing equipment (PSE) using Power over Ethernet technology, in order to find the maximum power that can be provided by the PSE.
The determination of power supplied by a PSE to an apparatus is a delicate operation since when providing an apparatus with a power lower than the required power, the voltage applied to the apparatus may be too low and the apparatus may be damaged by too high a current.
The present invention is directed to providing an improved power management module for managing power supply to an apparatus, making it possible to enhance the prevention of damaging an apparatus powered up by the power management module.